The guards were killed Friday night near the city of Saravan along the Iranian border with Pakistan, CNN reported.
It was unclear whether those executed were in custody before the attack or if they were rounded up after, The New York Times said.
"We had issued warnings previously that bandits and anti-Iran group members who commit acts causing damage to innocent people or security and military personnel will face reciprocal action by us," local attorney general Mohammad Marzieh said.
He said the hangings were "in retaliation for the martyrdom" of the guards.
Rajabali Sheikhzadeh, deputy governor of Sistan and Baluchestan province, said the attackers fled into Pakistan after the confrontation with the guards, the Iranian news service FARS reported.
The number of casualties sustained by the rebels was unknown, Sheikhzadeh said.
The area where the attack took place stands at the border shared by Iran, Pakistan and Afghanistan and has proved a hotbed of Sunni rebels opposed to Iran's Shiite-led Islamic Republic, the Times said. For decades, the area has resembled a war zone and violence against Iranian government installations is fairly common.
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